The term "electrical machining" is herein intended to refer to electroerosion or electrical discharge machining (EDM), electrochemical machining (ECM) and so forth and also, among others, to include electro-spark deposition (ESD) and arc welding, all of which processes are per se well known in the art.
Machines designed to perform electrical machining have hitherto commonly used a large-capacity transformer necessary to transform the magnitude of a commercial alternating-current (AC) source to an adequate level, the transformed AC being then rectified to provide a direct-current (DC) output which is in turn pulsed by switching means to produce a series of electrical pulses of a desired pulse duration, interval and frequency for application across a machining gap formed between a workpiece and a machining electrode. As is well known, the machining medium is water or oil in EDM and an electrolyte in ECM or electrodeposition processes where the pulsed application of electrical energy permits a high-current density machining or deposition. Since, however, the low-frequency commercial AC of a frequency ranging from 50 Hz to 60 Hz is utilized directly, it has been unavoidable that the transformer and the entire power supply unit is undesirably large in size and heavy in weight. Furthermore, the use of a reactor required for control purposes in this type of power supply is disadvantagous in that its response is relatively slow and most often unsatisfactory.
Apart from the above, the power supply for electrical machining requires, besides a main power supply for supplying the machining gap with machining energy in the form described, one or more auxiliary supplies which are small and hence different in capacity for operating or controlling the machine and machine components. This requirement for multiple inputs has further contributed to rendering the entire power equipment larger and heavier. Thus, power-supply units which have been proposed and in use heretofore are characterized by bulkiness and low efficiency and have left much desired.